I've already burned it for 24 hours and it is now giving the constant value of 932.36,pls tell me how to calculate the RZERO value.
From the datasheet here --->MQ135 datasheet, It is the value of Sensing resistor at 100 PPM of Ammonia(NH3) or from the graph in Fig. 3, you can use gases that has y intercept as 1 and appropriate concentration, i.e you need atleast some known parameter to get it. The legend in the graph is also not clear (as far as getting the values from the Log - Log graph, there are tutorials in youtube).
I'm also in need of solution to this, so far this is what I read on the internet... You need a chemistry lab to do it !!!